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https://github.com/rust-lang/chalk

An implementation and definition of the Rust trait system using a PROLOG-like logic solver
https://github.com/rust-lang/chalk

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An implementation and definition of the Rust trait system using a PROLOG-like logic solver

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# chalk



Chalk is a library that implements the Rust trait system, based on [Prolog-ish][Prolog] logic rules.



See the [Chalk book](https://rust-lang.github.io/chalk/book/) for more information.



## FAQ



**How does chalk relate to rustc?** The plan is to have rustc use the

`chalk-solve` crate (in this repo) to answer questions about Rust programs, for

example, "Does `Vec` implement `Debug`?". Internally, chalk converts

Rust-specific information into logic and uses a logic engine to find the answer

to the original query. For more details, see

[this explanation in the chalk book][chalk-lowering-details].



**Where does the name come from?** `chalk` is named after [Chalkidiki], the area where [Aristotle] was

born. Since Prolog is a logic programming language, this seemed a

suitable reference.



[Prolog]: https://en.wikipedia.org/wiki/Prolog

[Chalkidiki]: https://en.wikipedia.org/wiki/Chalkidiki

[Aristotle]: https://en.wikipedia.org/wiki/Aristotle

[chalk-lowering-details]: https://rust-lang.github.io/chalk/book/#chalk-works-by-converting-rust-goals-into-logical-inference-rules



## Blog posts

[blog-posts]: #blog-posts

Here are some blog posts talking about chalk:



- [Lowering Rust Traits to Logic](https://smallcultfollowing.com/babysteps/blog/2017/01/26/lowering-rust-traits-to-logic/)

    - Explains the basic concepts at play

- [Unification in Chalk, Part 1](https://smallcultfollowing.com/babysteps/blog/2017/03/25/unification-in-chalk-part-1/)

    - An introduction to unification

- [Unification in Chalk, Part 2](https://smallcultfollowing.com/babysteps/blog/2017/04/23/unification-in-chalk-part-2/)

    - Extending the system for associated types

- [Negative reasoning in Chalk](https://aturon.github.io/blog/2017/04/24/negative-chalk/)

    - How to prove that something is not true

- [Query structure in chalk](https://smallcultfollowing.com/babysteps/blog/2017/05/25/query-structure-in-chalk/)

    - The basic chalk query structure, with pointers into the chalk implementation

- [Cyclic queries in chalk](https://smallcultfollowing.com/babysteps/blog/2017/09/12/tabling-handling-cyclic-queries-in-chalk/)

    - Handling cyclic relations and enabling the implementation of implied bounds and other long-desired features in an elegant way



## REPL



There is a repl mainly for debugging purposes which can be run by `cargo run`. Some basic examples are in [libstd.chalk](libstd.chalk):

```bash

$ cargo run

?- load libstd.chalk

?- Vec>: Clone

Unique; substitution [], lifetime constraints []

```



## Contributing



If you'd like to contribute, consider joining the [Traits Working Group][working-group].

We hang out on the [rust-lang zulip][rust-lang-zulip] in the [#wg-traits][wg-traits-stream] stream.



See [the contributing chapter][contributing] in the chalk book for more info.



[working-group]: https://rust-lang.github.io/compiler-team/working-groups/traits/

[rust-lang-zulip]:https://rust-lang.zulipchat.com

[wg-traits-stream]: https://rust-lang.zulipchat.com/#narrow/stream/144729-wg-traits

[contributing]: https://rust-lang.github.io/chalk/book/contribution_guide.html